1. Field of the Invention
This invention relates to a dispenser for dispensing atomized fluids under pressure, provided with a shut-off element operated by the action of the pressurized fluid.
2. Discussion of the Background
To dispense pressurized liquids in finely atomized form it is known to use manually operated pumps with a hollow liquid exit stem on which a dispensing head is mounted incorporating a chamber at which the pressurized liquid arrives from the pump stem. The pressurized liquid is dispensed in atomized form after passing through a discharge hole in which a series of spiral channels are provided leading to a chamber wherein the fluid undergoes a strong swirling movement before being expelled to atmosphere.
To achieve good and constant atomization without liquid dripping from the outside of the discharge hole the liquid pressure at this hole, when dispensing commences, must be sufficiently high from the beginning. This problem has been previously partially solved by constructing and using pumps from which the liquid emerges only when its pressure is sufficiently high.
Such pumps are, however, of rather complex structure and their cost is fairly high. In addition the liquid delivered by the pump tends to lose pressure as dispensing commences, in traversing the various passages provided in the dispensing head.
If the fluids to be dispensed tend to dry, so obstructing fluid passage through the discharge hole (which very easily happens, for example, if the fluid is hair lacquer, dressing fluid or the like), the discharge hole must be closed on termination of each dispensing operation in order to isolate from the air the fluid residues present between the pump and the discharge hole in the dispensing head.
To overcome this problem, U.S. Pat. No. 4,182,496 describes a dispensing head having a compression chamber housing a slidable piston with an appendix extending towards a discharge hole provided in an insert delimiting the compression chamber. Acting on the piston there is a spring which when under rest conditions urges its free end against said insert to hermetically seal the discharge hole, hence isolating any fluid present in said chamber from contact with the air. When the pump is operated, the pressurized fluid reaching said chamber causes the piston to move against the action of the spring, with consequent withdrawal of the free end of its appendix from the discharge hole.
The dispensing head of U.S. Pat. No. 4,182,496 and that (analogous but less sophisticated) represented in DE-A-1750186 have the drawback that even if the liquid reaches a high pressure in the compression chamber before the movable piston begins to move from its rest position by overcoming the action of the spring which acts on it, there is in any event some dripping of the liquid (consequent from a considerable reduction in its pressure) passing through the discharge hole on commencement of dispensing (with consequent formation of incrustations on the outside of the discharge hole). A similar negative phenomenon occurs immediately before the piston appendix closes the discharge hole on termination of each delivery.
In this respect, on commencement of dispensing, when a certain pressure is reached in the compression chamber the piston begins to gradually move, with gradual withdrawal of the end of its appendix from the discharge hole to gradually open liquid passage to the discharge hole. The discharge hole is completely free only after the free end of the piston appendix has moved sufficiently far from it. However before this position is reached a certain quantity of liquid will already have emerged through a narrow path causing it to lose pressure.
The reverse phenomenon occurs when delivery ceases.